The fine structural aspect of primate (Macaca mulatta) corpus luteum (CL) was examined at termination of pregnancy. Corpus luteum was obtained from 1) intact, 2) hypophysectomized and 3) fetectomized monkeys. The fine structural observations showed that the CL from hypophysectomized and fetectomized animals showed only minor variation from the intact ones, and that the granulosa lutein cells in all three groups of animals possess fine structural characteristics essential for steroidogenesis.